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Old Jul 28, 2012, 11:58 AM
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John235
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What are your thoughts on the weight distribution
You always ask great questions, John. This model was conceived with the idea of a central COG with the twin motors very close to it. The fuselage from nose to rudder line is 43.25 inches and the COG was placed at 22 inches from the nose. The rudder leverage is about 21.25 and the elevator leverage is about 13 inches from estimated center of lift to the COG. A 43 inch wingspan was chosen to fit easily into my sedan as was the 46.5 inch overall length. The canard span is 25 inches and its area was increased as the main wing's area was decreased until the Canard COG calculator indicated the desired COG position. The vertical COG desired position was at the thrust line or slightly below to avoid nose over landings. This was accomplished by lowering the 8 ounce battery to mid fuselage. The rear wing was lowered from the canard's elevation in an effort to put the thrust line at the center of vertical drag which was mainly from the canard and the landing gear. Considering the vertical static torques about the COG, the main wing weighs 16 ounces and it's balance point is 8 inches from the COG giving a torque of 16 times 8 or 128 ounce inches. The canard battery combination is 13.3 ounces at about 10 inches max from the COG giving 133 ounce inches which comes close the desired resultant. Knowing these numbers as the building progressed, dictated the placement of parts on the remainder of the model. Happily, the completed model less wings and battery balanced very near to the COG. The balance and alignment of the Twin turned out better than any of my previous models and I am at a loss to try and surpass it. On the maiden flight which was a straight line to 3 feet in the air then down, it required only power and brief rudder control at the start. My transmitter now stands at two clicks of down trim.

Looking back over the last seven years, I can see the progress made on 23 of my canard designs all of which were influenced by the help of you John and many others. I am truly grateful for each and every one of you for sharing your experiences with me.

John235
Quote:
Have you noticed any benefit of having the engines and battery located close to the COG?
The spinner tips are at the COG and the motors will add to the lift of the wing to protect it from stalling The eight ounce battery was placed to balance the model and ended up having it's output surface about one inch to the rear of the canard's TE. The central balance point is ideal IMHO. The inertia of the battery up front could be a matter of concern.

Charles
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Last edited by canard addict; Jul 28, 2012 at 07:36 PM. Reason: To somewhat clarify.
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Old Jul 29, 2012, 11:42 AM
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Your welcome Charles!
sorry it's been a while, I'm packing out for a move due to (pdf) hassles at the apartment-will be going into a home with double the factory space, and getting a fresh start on everything!
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Old Aug 03, 2012, 04:30 PM
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Duck Twin Weight Distribution

John 235
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What are your thoughts on the weight distribution?
My last reply to this question did not fully answer John's question. To clarify my answer, a 1/4 scale drawing was made to illustrate the vertical static weights and the lifts of the wings. The wings were removed from the model to find more accurate positions of their CG's. The symbols used are defined as follows:
W1 = combined canard and battery weight, W2 = weight of main wing assembly, W3 = fuselage weight. L1 = canard lift, L2 = main wing lift. The vertical position of the CG was estimated from handling the finished model and the chuck glider.the thrust vs drag rotational forces about the CG were judged to be within reasonable limits. The centers of lifts of the wings were placed at 1/3 chord. The canard area is 145.4 sq. inches and it's load is 17.6 ounces per sq. ft.
The wing area is 286 and it's load is 13.7. I hope the two posts together have shown the weight distribution. There is plenty of payload space between the two wings. A canard was chosen for a recent design of an electric full scale battery/ gas hybrid due to it's large payload space. It was in May 2012 of Popular Science.

Charles
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Last edited by canard addict; Aug 03, 2012 at 04:44 PM. Reason: Correction
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Old Aug 05, 2012, 06:50 PM
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Hi Charles, I am sorry for my late reply. The biggest difference I see with the twin engine layout, is the moment of inertial will be less, because the heaviest items such as battery and motors are located close to the COG. In theory, the smaller moment of inertia should be better for yaw damping, and maybe also have an effect on pitch stability of the model as the airspeed drops towards the canard stall. I asked because I was curious if any of these differences can be noticed in the flight characteristic of the model.

I've greatly enjoyed watching the development of your models so far. I'm always surprised when you have built yet another unique and interesting model. It happens just when I thought all the ground had been covered already. The four wheel landing gear is another interesting one. I can now see the attraction of having the model finely balanced on the center two wheels.
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Old Aug 05, 2012, 10:06 PM
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John 235
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The biggest difference I see with the twin engine layout, is the moment of inertial will be less, because the heaviest items such as battery and motors are located close to the COG. In theory, the smaller moment of inertia should be better for yaw damping, and maybe also have an effect on pitch stability of the model as the airspeed drops towards the canard stall. I asked because I was curious if any of these differences can be noticed in the flight characteristic of the model.
Yes, as we have discussed, the thrust line should pass through the vertical cog and the mid engine also ideally puts it close to the horizontal cog as I see it. The inertia's of the battery and nacelle power units which are close to 1/3 of the model's weight, could cause yaw oscillation about the cog but the large vertical stabilizers seem to have good preventive control. The battery, which is 18% of the model's weight, probably has it's influence on pitch stability harnessed by the 50% canard. Regarding the flight characteristics: so far it has tested well without any problems. With it's better load distribution compared to my previous models, it has performed better than my expectations. The building and flying have had lots of pleasant surprises. There has been only two opportunities in this hot Summer to test the Twin. With cool clear Fall days approaching there will be better conditions to learn more about it.

John 235
Quote:
I've greatly enjoyed watching the development of your models so far. I'm always surprised when you have built yet another unique and interesting model. It happens just when I thought all the ground had been covered already. The four wheel landing gear is another interesting one. I can now see the attraction of having the model finely balanced on the center two wheels
Thanks, John, It means a lot to read those words from you. I am always interested in new ideas and can now see why designers put engines on wings.

Charles
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Old Aug 07, 2012, 11:21 AM
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edwen303


I feel that your Shinden's wings were both into near stall or what I call a mush condition. This may have been due to an under sized canard for a model and a CG point back into the main wing. That was the case with my Hobby Lobby International foam Shinden. At low speed the model would assume a nose up mushing position and slowly land itself. I found that a model plane needs a larger than scale horizontal stabilizer to give adequate lift at low speeds because the Reynolds number gets too low with a small chord. My Shinden was slow and light weight and the small canard was sluggish so an extra cell and more area was added to the canard which moved the CG forward. The discussion of my Shinden can be found in this thread and I hope it agrees with my recollection. It was passed on to Happymcc who may still be flying it.

The Duck Twin received red tip fins today to improve it's visibility.

Charles
Thanks Charles for the analysis! I liked how the Hobbylobby Shinden flew, slow and stable, even inverted. I simply keep my Shinden speed up and never had any problem since. That stall took place when I rolled her for inverted flight but applied too much down elevator, causing her nose up at medium throttle, then had a moment of scare. That was my maiden + 2 or 3 flight, so pretty scary...

Need to study fluid dynamics to understand Reynolds number . I am experimenting inverted gull wing type flying wing, so far not stable in flight, perhaps because of the short chord. Increased swept angle really helped the stability.

Question: Did you use or read about using Canard as elevon type control, aka, control both elevator and aileron. I have a Phase 3 F-16, very happy with her all-flying stabilator setup. Had a crash of the older version of F-16, so now I have a set of repaired airframe to mod, thinking about puting all-flying stabilator forward (canarvon?!), any insights?
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Old Aug 08, 2012, 06:14 AM
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edwen303
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Question: Did you use or read about using Canard as elevon type control, aka, control both elevator and aileron. I have a Phase 3 F-16, very happy with her all-flying stabilator setup. Had a crash of the older version of F-16, so now I have a set of repaired airframe to mod, thinking about puting all-flying stabilator forward (canarvon?!), any insights?
edwen, Please check out the discussion on pages 53 through 56 regarding elevons for short coupled canards. Page 56, post 833 shows the schematic.The system worked well on my D squared and Delta Duck models. I prefer the elevator type control up front over the all moving version. My experience with a flying wing is limited to the Zagi which was flown stock.

Charles
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Old Aug 08, 2012, 10:33 AM
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Thanks Charles! Both wing and canard using elevon must give you plane lot of maneuvability .

What I meant, now thinking not too bright idea, is the canard alone being the elevon. The picture in my post is for my current F-16. My plan with the repaired airframe is to move the wing backward and stabilator forward. The wing will not have elevator nor aileron. The canard will be made of two separate all-flying surface, the elevon setup. Looks like a Eurofighter,
http://media.defenseindustrydaily.co...derview_lg.jpg
but canard is much larger here and the all-flying elevon should give good pitch and yaw control, maybe even roll quick enough.
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Old Aug 09, 2012, 06:22 AM
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edwen 303
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What I meant, now thinking not too bright idea, is the canard alone being the elevon. The picture in my post is for my current F-16. My plan with the repaired airframe is to move the wing backward and stabilator forward. The wing will not have elevator nor aileron. The canard will be made of two separate all-flying surface, the elevon setup. Looks like a Eurofighter,
http://media.defenseindustrydaily.co...derview_lg.jpg
but canard is much larger here and the all-flying elevon should give good pitch and yaw control, maybe even roll quick enough.
Interesting project, edwen. I would put maximum distance between the wings. Please let us know of your results.

Charles
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Old Aug 09, 2012, 03:01 PM
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edwen 303


Interesting project, edwen. I would put maximum distance between the wings. Please let us know of your results.

Charles
Your D squared are actually more interesting: how did she respond if the wing elevon function is unplugged? The reason I ask is that would be the idea I am thinking for the canard F-16.
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Old Aug 09, 2012, 04:52 PM
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Edwen 303

I'm watching but I'm not placing any bets. Why would you want to put the roll control on the smaller wing, further from the CoG?

Vive la Difference! What I mean is: it's experiments that make life interesting. Keep trying new ideas. Aeroplanes more than anything are open to so many configurations.

Best of luck.

Nick
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Old Aug 09, 2012, 06:19 PM
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edwen, I hesitate to give positive comments on the behavior of models built with new ideas because of being proven wrong several times on this thread. My D Squared and Delta Ducks both worked well with elevons on both wings.The Firebat, page 53 post 791 was a disaster because I used a fast motor which apparently stalled the all moving canards which had a small lever arm about the CG with ailerons rear. The D Squared has the CG at the center of the fuselage, the canard hinge line forward of it by 6 inches and the main wing's hinge line 11 inches to the rear.
I flew it yesterday and was able to rotate it about the CG to land on the rear wheels nose high. Without the UP reflex at the wing's TE, it probably would not have worked. Flying it without those controls would be risky. If your F16 is light weight foam it will be advantageous. The Eurofighter has rear elevons from what I have read.

Charles
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Old Aug 17, 2012, 08:57 PM
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Tried a close coupled canard on my pseudo delta and she flew really nice. My first model to not drop the nose in turns! It's outer wings are 33 degree delta, flat, aprox 5% wing with round LE.
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Old Aug 18, 2012, 05:24 PM
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http://www.modelflying.co.uk/forums/...s.asp?th=24655

Okay canardly fliers. I did this on my iSpendPad, so it might even work. The link above goes to a UK real world magazine's Online thingy. The designer of the 'Cucumber, Doug McHard, was one of England's finest aeromodellers, who did stranger things with free flight models than most would dare to try with RC. Cucumber was one of Doug's more advanced - he practiced on several single engined monoplane canards before this one.

Enjoy

Dereck
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Old Aug 18, 2012, 08:17 PM
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Doug's Biplane design looks nice. It looks like it could also work with tail-dragger landing gear. I am eagerly waiting for Charles' four wheel trend to catch on. Who knows it might even be possible to make a sea-plane based on this..
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